Hacking chunks off of these reefs and bringing them back to the lab—where they subjected them to a bit of geochemical wizardry*—Finnegan’s team discovered an abrupt drop of about 5 degrees Celsius in the tropical ocean at the end of the Ordovician. Five degrees might not sound like a mass extinction, but the rocks say otherwise. “The general consensus in the field is that the Ordovician mass extinction is closely tied to climate change,” he said.
